This invention relates generally to glycol base engine coolants which are commonly used in internal combustion engines. More particularly, the present invention relates to an apparatus and a process for recycling used engine coolant.
Engine coolants which are conventionally employed to lower the freezing point or increase the boiling point of water in internal combustion engines commonly contain ethylene glycol as the base or primary additive component. Engine coolant typically has a glycol concentration of 40 to 70% concentration in water. When engine coolant is added to an internal combustion engine cooling system in sufficient concentration, the resulting coolant fluid provides protection against freezing to below -30.degree. F. and protection against boiling to an excess of 200.degree. F. While engine coolants are universally used in fluid cooled internal combustion engines, there are significant limitations to the useful life of such coolants. The glycol components of the coolant over time chemically break down into organic acids such as, for example, glycolic, formic and glyoxolic acids. The pH factor of the engine coolant composition also gradually decreases over time from a pH of approximately 10.
The coolant solution circulation through an engine cooling system under certain conditions produces a highly corrosive effect on all metals within the cooling system. When the pH factor decreases below approximately 8.3, the corrosive process forces steel and iron from the coolant system components into solution and also results in aluminum pitting. It has also been established that copper corrodes upon extended exposure to the engine coolant solution and also eventually dissolves into the solution. Zinc, which is conventionally employed to strengthen the solder in radiators, weakens due to engine coolant exposure so that leaks develop in the coolant system. In addition, over time the engine coolant concentration of potentially damaging suspended particulate matter, including corrosive products, dirt, silt and hard water salt deposits increases.
Because of the well established corrosive effects of the circulating coolant, corrosion inhibitors are conventionally added directly to the engine coolant. Over a period of time, the inhibitors are consumed and the engine coolant eventually produces significant corrosive effects throughout the coolant system. Consequently, the implementation of certain maintenance procedures is required for extended coolant usage. The most common procedure is to remove and replace the engine coolant composition after a pre-established time period. In some instances, cooling system additives, which are alkaline and include corrosion inhibitors, are directly added to the coolant to enhance the coolant properties, decrease the corrosive effects and postpone replacement of the coolant.
Recycling used engine coolant has become increasingly advantageous due to two significant factors. First, engine coolant, and in particular ethylene glycol, in some states and localities has been designated a hazardous waste. Federal and state environmental protection agencies have instituted strict regulation of the disposal of used engine coolant. In some cases, the disposal of engine coolant requires imposition of waste disposal fees and surcharges. Secondly, ethylene glycol, the principal component of engine coolant, has also become an increasingly more expensive product. In some instances, there have been significant shortages in the supply of ethylene glycol. Consequently, there are economic pressures to recycle engine coolant and recover the ethylene glycol component in an efficient and cost effective manner.
A number of processes and systems have been advanced as possible commercially viable solutions to the desirability of recycling engine coolant. Most of the processes have employed ion exchange and/or distillation techniques in various forms. Distillation of used engine coolant produces an acceptable end product but is relatively expensive and is a relatively slow process which is not very suitable for small onsite service centers. The distillation equipment is relatively capital intensive and requires significant energy consumption. In addition, relatively complex chemical and filtering techniques have been employed apart from and in conjunction with distillation for recovering and recycling used engine coolant. Quality control has also been a significant problem associated with some commercial engine coolant recycling systems.
U.S. Pat. No. 4,946,595 discloses a process for physically and chemically treating used engine coolant of a type which contains one or more glycol and/or alcohol based antifreeze components. The disclosed process includes the steps of oxidation with one or more known oxidizing agents, precipitation with one or more known salt forming agents, as well as filtration. Chemical additives are added to enhance the oxidation and precipitation. Various corrosion inhibitors and buffering agents are also added to adjust the pH of the recovered solution.